Magnetic core



Sepe 17, 1946o a. H. scLATER 2,407,688

MAGNETIC CORE HIS Attorney.

SePt- 17, 1946- i l l. H. SCLATER 2,407,688

MAGNETIC CORE ,Filed Dec. 3o, 1942 2 sheetssheet 2 Pgs.

7 52 1 a as if 7/ t I/ 57 l 7 'I ZZ \`0 d a Inventor:

lvnhoe HSda-te, b Wa/y 'C /MM y His Attorney.

Patented Sept. 17, 1946 MAGNETIC CORE Ivanhoe H. Sclater, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application December 30, 1942, Serial No. 470,579

(Cl. F75-356) 7 Claims. l

My invention relates to laminated magnetic core structures for electrical induction apparatus such as transformers and reactors.

In the usual construction of magnetic cores, the laminations are cut or punched from relatively large stock sheets which are produced by rolling from bars or billets of a suitable magnetic material, such as variousI steel alloys, such as silicon steel or a magnetic nickel iron steel. It is known that the rolling process produces a grain structure in sheets which may extend in the direction in which the sheets have been rolled. It is further known that the path of least magnetic resistance of such material is generally in the di* rection that the sheets have been rolled, though in certain types of steels the most favorable magnetic direction, in so far as low flux losses are concerned, may be at some angle with respect to the direction of rolling. Thus, it will be seen that for optimum results for magnetic cores it is desirable to cut the laminations from sheets of magnetic material so that the core flux path is parallel with the path of least magnetic resistance, or parallel with the direction of rolling even at the corners.

One common form of magnetic core consists of a stack of L shaped punchings, but it will be apparent that such shapes cannot be punched as a single piece from a standard stock in such a manner that the most favorable magnetic direction extends parallel with the flux path in both parts of the punchings. This is due to the fact that the grain extends in the same direction throughout all parts of the stock While the two parts of the L shaped punchings are at right angles to each other. Another common form of a core consists of a rectangular core with adjacent laminations being stacked at right angles with respect to each other. While the most favorable magnetic direction of this type of core may be made parallel with the direction of the flux path throughout the central portion of the laminations, the core flux must be cut crosswise of the most favorable direction at the ends of the laminations in traversing from one core leg to the next. Due to this cros'swise flow of iiux at the corners of the core, relatively high losses occur at these points.

One way of overcoming the difculties referred to above is to provide a core structure by winding a ribbon of suitable magnetic steel so that there will be no joints and so that all the flux will pass parallel to the direction of rolling of the material or in the direction which has the least magnetic reluctance. Such a type of wound core has been found to be very successful in the production of relatively small size transformers, which are called distribution transformers in the trade, Due to the various mechanical difficulties, however, it has been less economical to Wind much larger sizes of ribbon sheet material so as to produce sufficiently large cores for electrical apparatus having a high kva. capacity.

Another way of providing cores of laminated material in which the direction o-f flux path is along the line of least magnetic reluctance in the Vicinity of the joints is to assemble the laminations, each corner of which has been cut on the diagonal, so as to provide a mitered joint at each of the corners. It will be seen, however, that when each of the joints at the various corners of the rectangular core are coincident with the diagonal running from the inside corner to the outside corner all of the joints will be in substantial registry so that the possibility of gaps being formed at the joints for increasing the magnetic reluctance is appreciable, even though elaborate means are provided for clamping the magnetic laminations together.

An improved arrangement for providing mitered joints at the various corners of the assembled laminations and for preventing separation at the joints is described and claimed in patent application S. N. 376,304, Graneld, filed January 28, 1941 (now Patent 2,348,003 dated May 2, 1942), and assigned to the same assignee as this present invention. In that application there is described a stacked laminated core formed of laminations which have mitered butt joints with extensions and corresponding indentations in the edges of the adjacent laminations, so as to prevent an appreciable gap from being formed at the butt joint. The various layers which are stacked to form the core are made up of similarly assembled laminations which are oppositely arranged so as to stagger the adjacent joints of contiguous layers. In this manner there will be a minimum of magnetic flux which will pass crosswise of the most favorable magnetic direction and due to the projections and corresponding interfitting indentations which may extend in opposite directions for the adjacent joints of contiguous layers an overlapping'vvill be provided at the joints so as to substantially preclude separation of the laminations of the assembled core.

There is also described in an application S. N. 470,578 to Brand, filed concurrently herewith, and assigned to the same assignee as this present invention, a corner construction which provides a minimum of magnetic reluctance at the corners and which also provides overlap so as to minimize separation of the `stacks of the assembled core. In the construction cf this application mitered butt jo-ints are provided at the corners of each layer of laminations, the joints between laminations of one layer being displaced or offset from the adjacent joints of a contiguous layer. The offsetting is obtained by cutting one edge of each of the laminations on a diagonal so that the joints will be coincident with the diagonal running from the inside to the outside corner of the assembled laminations and cutting the other ends of the laminations with a mitered butt joint which is offset or displaced from a diagonal running from the inside corner to the outside corner of the assembled laminations. These latter joints are obtained by notching the corner or providing a rst portion which is parallel with a longitudinal axis of the assembled core and a second portion of a corner which is parallel with the diagonal. The laminati-ons are then stacked to provide layers, and the layers are oppositely arranged so that the joints between laminations of one layer will be offset from joints between laminations of a contiguous layer. Thus, a joint between laminations of one layer which is coincident with the diagonal will be adjacent to but staggered from a joint of the adjacent or contiguous layer which i's orfset from the diagonal.

In application S. N. 470,583 Welch, filed concurrently herewith and assigned to the same assignee as the present invention there is described an improved magnetic core in which each of the corner joints are mitered and the adjacent joints between laminations of contiguous layers are offset on opposite sides of a diagonal running from the inside corner to the outside corner of the assembled laminations. In this manner with such a construction a minimum of flux path is provided which is at an angle to the most favorable magnetic iliux direction. 'Ihis construction is obtained by notching the joints with the broken line joints having a small portion of the joints parallel with the longitudinal axis of the assembled laminations and the adjacent joints between laminations of a contiguous layer has a small portion which is parallel with the lateral axis of the assembled laminated coie.

It is, therefore, an object of my invention to provide a laminated core of the types described aibove with an improved construction which will have a relatively small resistance to the flow of flux at the corners of the assembled lamination, and which will have a corner shaped so as to facilitate assembly of the laminations.

Another object of my invention is to provide a new and improved core construction in which the laminations are so cut from metal stock that when tted together into a unit, the core flux may iiow in the most favorable magnetic direction of the laminations throughout a large portion of the magnetic circuit.

A further object of my invention is to provide a core construction having separate laminations with a corner construction such as to facilitate the manufacture thereof as well as to provide an enicient assembled core construction.

A further object of my invention is to provide an improved corner construction for a laminated magnetic core so that the reluctance of the joint varies in a direction and to an extent to make a substantial reduction in inequality of total magnetic reluctance along the loops of different lengths of magnetic ilux paths of the core.

Further objects and advantages of my invention will become apparent from the following description referring to the accompanying drawings, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In the drawings Fig. 1 is an exploded perspective view of layers of assembled laminations, the laminations being formed in accordance with an embodiment of my invention; Figs. 2 and 3 illustrate curves which will be employed in the description of my invention; Fig. 4 illustrates a method of stam-ping the laminations employed in the construction of Fig. 1 from ribbon of magnetic material with a minimum of waste; Fig. 5 is a perspective View of a three-legged core which is provided with an embodiment of my invention, and Fig. 6 illustrates a method whereby the laminations employed in Fig. 5 may be out from a ribbon of steel with a minimum of waste.

Referring to Fig. 1 of the drawings I have illustrated a magnetic core having a plurality of layers of stacked laminations. Any suitable number of layers may be used depending upon the size of the core which is desired. Each of the layers includes a plurality of separate laminations which are closely fitted at their ends forming butt joints. Any suitable number of laminations may be employed to form each of the layers, and in the construction illustrated in Fig. 1, four such laminations are employed to form a single layer o-f what may be called a single phase core for a suitable electric induction apparatus, such as a transformer.

It is to be understood, however, that a core having any suitable number of legs and yokes may lbe formed according to my invention. Thus, in Fig. 1 I have illustrated a layer IU including laminations I I and I2 which may be called leg sheets and laminations I3 and I4 which may be termed yoke sheets. It is to be understood, however, that the leg sheets II and I2 could be yoke sheets and the yoke sheets I3' andv I4 could be the leg sheets, if desired. The various laminations may be formed from strip material having the most favorable magnetic direction lengthwise of the strip so as to provide a core with a minimum. magnetic reluctance. 'I'hese laminations could be punched with a 45 degree angle at the ends and thus attempt to provide substantially no path in the corners through which the flux must pass crosswise of the most favorable direction. However, as has been stated above, if all the joints are in substantial registry there is considerable difficulty in preventing gaps from being formed at the butt joints, even though elaborate clamp-ing arrangements are provided. In order, therefore, to provide an assembled laminated structure which not only has a minimum reluctance at the corners, but which also is formed so as to provide overlapping between adjacent laminations of contiguous layers so as to maintain the tightness of the joints throughout normal use of the device, I provide corner constructions which not only have a substantially mitered or diagonally extending butt joint but the edges of the laminations which form the joints are so out and so assembled as to be displaced or offset from the adjacent joints of the contiguous layer of laminations and thereby provide overlapping. Thus, the lamination I I is formed with an end I5 which is cut at an angle of less than 45 degrees with an axis of the assembled laminations. In Fig. l it will be seen that I have shown the edge I5 which is out at an angle of substantially 30 degrees with the longitudinal axis of the assembled laminations. The other end of the lamination I I has an end IB, the surface of which makes an angle of less than 45 degrees with the lateral'axis of the assembled laminations. Thus, as will be seen in Fig. l the end I6 makes an angle of approximately 30 degrees with this lateral axis. In order to provide a relatively tight butt joint between the edge I6 and an adjacent edge I1 of the lamination I3, it will be seen that the edge I1 is also cut at an angle which is less than 45 degrees withvthe lateral axis, or 30`degrees as is illustrated in Fig. 1. The opposite end of the lamination I3 has an edge surface I8 which is cut at an angle less than 45 degrees with the longitudinal axis and in Fig. 1 it will be seen that lthe angle is about 30 degrees. It will also be seen that the lamination I2 is similar tothe lamination II, it only being oppositely disposed in assembled condition with respect to the lamination II. Thus the lamination I2 has an edge surface I9 which abuts against the adjacent surface I8, the surface I9 making a similar angle of 30 degreeswith a longitudinal axis while the opposite edge surface 2G of the lamination I2 makes an angle of 30 degrees with the lateral axis of the assembled lamination. Furthermore, the lamination I4 is similar to the lamination kI3 except beingoppositely arranged in an assembled condition. Thus, the lamination I has an edge surface 2| which abuts against the surface Zii and is therefore at an angle of 30 degrees with a lateral axis while the oppositeedge surface 22 of the lamination I4 abuts against the surface I5 of the lamination II and, therefore, makes an angle of 30 degrees with a longitudinal axis.

Since the layer of lamination IE! has butt joints all of which are offset on one side of diagonale running from the inside corners to the outside corners of the assembled laminations at the various corners as is shown in Fig. 1, by forming an adjacent layer 25 of laminations similar to those employed to form the layer I and then stacking the layers so that the layer 25 is reversed or oppositely arranged with respect to the layer I0, the joints at each of the corners will be offset from each other so as to provide overlapping at the various laminations of each layer with the adjacent laminations of a contiguous layer in the vicinity of the joint. Thus adjacent laminations have diagonal butt joints at adjacent ends with at least a major portion thereof being a straight line and running from `the vicinity of the inner corner to the vicinity of the outer corner of the assembled laminations. With this construction it will be seen that the slight overlapping will accomplish the mechanical results of substantially preventing separation of the laminations and thereby minimize the possibility of gaps being formed at the butt edge. It will also be seen that the joints between adjacent laminations of contiguous layers are not only oppositely but symmetrically disposed on either side of the diagonal running from the inside corner to the outside corner of the assembled laminations. Thus adjacent butt joints of two superimposed layers form an acute angle with each other to provide overlapping which tapers in a direction crosswise of the laminations and toward the shorter perimeter of the core.

lAlthough the lamination layers in Fig. 1 are shown with each contiguous layer being oppositely arranged with respect to the adjacent layer, it is to be understood that any suitable number f layers, if desired, may be stacked so that the joints are in registry and then stack'another suitable number which are oppositely disposed with respect to the rlrst group. In any case there will always be two contiguous layers which are oppositely arranged so as to provide an offset at the joints between these layers.

It will be seen that with a plurality of layers of laminations formed in the manner described above a relatively small amount of iiux at the edges will pass crosswise of the grain, and with such a construction considerable improvement in efficiency is obtained over that in which the laminations are formed with overlapping rectangular joints. This is illustrated in Fig. 2 in which the curve 35 illustrates the per cent loss in the core joints of the conventional joints having rectangular overlappings while the curve 3S illustrates the loss in the core joints with joints made according to my invention. In Fig. 2 the per cent core loss is plotted as abscissa and the per cent flux density is plotted on the ordinate axis. In order to further show the improvement in operation of cores formed according to my invention over those formed with rectangular shaped laminations I have illustrated in Fig. 3 the characteristics in which the per cent exciting current is plotted as abscissa and per cent density plotted as ordinate. Curve 31 illustrates the characteristics of a conventional core having rectangular ends while curve 33 represents the characteristics of a core formed with my improved joint construction.

A further advantage of tapering the joints of the corners in the manner described above is that the overlap is wider at the longer perimeter of the core and narrower at the shorter so that the joint reluctance of the core is a little less at its longer perimeter and therefore tends to compensate for the greater reluctance of the iron portion of the magnetic circuit along the longer perimeter, thus helping to equalize the total reluctance along each perimeter and thereby equalize the distribution of the flux, as the flux otherwise tends to crowd to the shorter perimeter of the core. A further advantage of my improved construction is that the joint has greater friction and stability'due to its relatively wider overlap near the outside perimeter.

Not only is a core formed with my improved laminations efficient in operation but the laminations may be formed from a constant sheet material with a relatively small amount of waste. I have thus illustrated in Fig. 4 a strip of magnetic material 4G having the most favorable direction of flux parallel with the axis as shown by the arrow. The various laminations may then be punched from this strip of magnetic material 40 with only two different dies and with a relatively small waste at every other cut. Thus in Fig. 4 I have illustrated the cutting of the lamination I2 with the edge I9. It will be seen that for instance the lamination I3 has an edge Il which may be cut along the edge which forms the edge I97 and the only waste will be relatively small rectangular portions c. Iy and 42. However, the opposite edge I8 of the lamination I3 has such a configuration that it is similar to an edge I6 of the lamination II. Thus no waste will result when making the cut to form the edges of half the laminations.

In view of the above it will be seen that I have provided an improved core construction formed of layers of laminations in which not only does the maximum of flux pass in the direction of most favorable magnetic conductance but overaxis of the assembled laminations.

lapping is provided at the ends so as to preclude separation at the butt joint. Furthermore the various layers may be formed of a similar Width or of an equal width and be punched from the same strip with only a relatively small amount of waste at every other punch. Furthermore, with my construction the corners are so formed as to provide no voids at the assembled corners of the laminated core.

It is to be understood that my invention may be applied to a core having any suitable number of laminations, per layer and in Fig. 5 I have illustrated my invention as applied to a three-legged core which may have application to a three-phase core including a plurality of layers each having seven assembled laminations, In the arrangement illustrated in Fig. 5 it will be seen that the various layers are made of similar laminations except that the laminations are stacked in reverse order in adjacent laminations to provide overlapping at the joints. The layer of laminations 50 includes an outer leg sheet 5l which has an edge 52 making an angle less than 45 degrees with the longitudinal axis which, in the illustrated embodiment of my invention, is 30 degrees, and an opposite edge 53 which makes an angle less than 45 degrees or 30 degrees with the lateral axis of the assembled laminations, Cooperating with `the leg sheet 5l is provided a yoke sheet 54 having an edge 55 which abuts the edge 52 and Y a yoke sheet 56 having an edge 51 which abuts the edge 53 of the lamination 5i. Another outer leg sheet 58 is provided having ends similar to the leg sheet 5I, the leg sheet 58 being oppositely arranged in the layer 50. Thus, the leg sheet 5B has an edge 59 which makes an angle less than 45 degrees with the lateral axis or 30 degrees and an edge 6e which makes an angle of less than 45 degrees or 30 degrees with the longitudinal Cooperating with the leg sheet 58 there is provided a yoke sheet 6l having an edge 62 which abuts the edge 59 and another yoke sheet 63 having an edge 64 which abuts the edge 5D of the lamination 58. A center leg 55 is provided having an edge 66 which makes an angle greater than 45 degrees or about 50 degrees with the lateral axis of the assembled laminations so that the leg sheet 65 may be punched from a strip of material having a width similar to that oi all the laminations and still be able to provide an edge El which is on a slight diagonal. An edge B8 is provided on the yoke sheet 5l' for cooperating with the edge 67 of the center leg sheet 65, Also, an edge 69 is provided on the yoke sheet 54 for abutting the edge 66 of the Acenter leg 65. The opposite end of the leg sheet 65 has a similar edge which is opposite to the upper end and includes an edge 'l0 which makes an angle greater than 45 degrees with the lateral axis oi the assembled laminations so as to provide a diagonal edge 1l even though the width of the leg sheet 65 is similar to the width of the remaining laminations. The yoke sheet B3 is also provided with a cut edge 'l2 which abuts the edge i and the yoke sheet 56 is provided with an edge 13 which abuts the edge 1| of the center leg sheet 55.

In Fig. 6 I have illustrated how the seven laminations may be cut from a ribbon of steel 'l5 with a minimum of waste. In Fig. 6 I have numbered the cut laminations similar to the numbers in Fig. and it will be seen that the yoke sheets 56 and 6| are similar, the leg sheets 5I and 58 are similar, and the yoke sheets 54 and 63 are similar. Thus a small amount of waste will be formed when cutting the edges between ther yoke sheet and the leg sheet 5l and a small amount of waste will be formed when cutting the edge between the yoke sheet 54 and the leg sheet 65. However, the various laminations may be cut from a ribbon of steel with a relatively small amount of waste.

Although I have shown and described particular embodiments of my invention, I do not desire `to be limited to the particular embodiments described, and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A magnetic core including a plurality of layers of assembled laminatons formed lengthwise from strip material having the most favorable magnetic direction lengthwise of the strip, adjacent laminations having a diagonal butt joint at adjacent ends, with at least a major portion thereof being a straight line and running from the vicinity oi the inner corner to the vicinity of the outer corner of the assembled laminations each of said laminations having a iirst joint edge surface at an angle of less than 45 degrees with a lateral axis of the assembled laminations and a second joint edge surface at the opposite end at an angle of less than 45 degrees with the longitudinal axis of the assembled laminations.

2. A magnetic core including a plurality of layers of assembled laminations formed lengthwise from strip material having the most favorable magnetic direction lengthwise of the strip, adjacent laminations having a diagonal butt`joint at adjacent ends with at least a major portion thereof being a straight line and running from the vicinity of the inner corner to the vicinity of the outer corner of the assembled laminations, each of said laminations having a first joint edge surface at an angle of less than 45 degrees with a lateral axis of the assembled laminations and a second joint edge surface at the opposite end at an angle of less than 45 degrees with the longitudinal axis of the assembled laminations, said laminations of each layer being assembled with a first joint edge surface of one lamination iitting a second joint edge surface of the adjacent lamination.

3. A magnetic core including a plurality of layers of assembled laminations formed lengthwise from strip material having the most favorable magnetic direction lengthwise of the strip, adjacent laminations having a diagonal butt joint at adjacent ends with at least a major portion thereof being a straight line and running from the vicinity of the inner corner to the vicinity of the outer corner of the assembled laminations, each of said laminationshaving a first joint edge surface at an angle of less than 45 degrees with a lateral axis of the assembled laminations and a second joint edge surface at the opposite end at an angle of less than 45 degrees with the longitudinal axis of the assembled laminations, said laminations of each layer being assembled with a first joint edge surface of one lamination iitting a second joint edge surface of the adjacent laminations, contiguous layers of said assembled laminations being oppositely disposed so as to provide overlapping of adjacent laminations of contiguous layers.

4. A magnetic core including a plurality of layers of assembled laminations formed lengthwise from strip material having the most `favorable magnetic direction lengthwise of the strip, ad-

jacent laminations having a diagonal butt joint at adjacent ends with at least a major portion thereof being a straight line and running from the vicinity of the inner corner to the vicinity of the outer corner of the assembled laminations, each of said laminations having a rst joint edge surface at an angle of about 30 degrees with a lateral axis of the assembled laminations and a second joint edge surface at the opposite end at an angle of about 30 degrees with the longitudinal axis of the assembled laminations.

5. A magnetic core including at least two superimposed layers of laminations, each layer including a substantially straight line butt joint in its magnetic circuit running from the vicinity of the inner corner` of the assembled laminations, and the butt joints of said two layers forming an acute angle with each other whereby a lamination of one layer overlaps the joint of the other layer, said overlap between said two joints being tapered in a direction crosswise of said 1aminations.

6. A magnetic core including at least two superimposed layers of laminations, each layer including a substantially straight line butt joint in its magnetic circuit running from the vicinity of the inner corner of the assembled laminations, and the butt joints of said two layers forming an acute angle with each other whereby a lamination of one layer overlaps the joint of the other layer, said overlap between said two joints being tapered in a direction crosswise of said 1aminations and tapered towards the shorter perimeter of said core.

7. A magnetic core containing at least two straight portions meeting at an angle and forming a corner, and including at least two layers of laminations, each layer including a generallydiagonal continuously straight line butt joint extending from the vicinity of the innercorner to the vicinity of the outer corner of the assembled straight portions, one of said joints terminating on one side of said outer corner and the other joint terminating approximately the same distance on the other side of said outer corner.

IVANHOE H. SCLATER. 

